Buttons will not be shown if you have "Limit allowed HTML tags and correct faulty HTML" filter enabled, you can disable this filter (security risk) or add to each element in "Allowed HTML tags" setting this few classes: <p class="text-align-left text-align-center text-align-right text-align-justify">. You must add "class" attribute to each element which you want to align.

Module Filter provides form element "text_format" and filter plugin (see FilterInterface), then Editor module alter text_format element and apply all editor plugins (see EditorPluginInterface) to this element, btw one of editor plugin contains in ckeditor module (see Drupal\ckeditor\Plugin\Editor\CKEditor)...
In few words: editor module is affects on input form through hook form alter, but can't affect on output filtering, because it's in responsibility of filter module.

Drupal 8.0.6 was released on April 6 and is the final bugfix release for the Drupal 8.0.x series. Drupal 8.0.x will not receive any further development aside from security fixes. Drupal 8.1.0-rc1 is now available and sites should prepare to update to 8.1.0.

Drupal 8.1.9 was released on September 7 and is the final bugfix release for the Drupal 8.1.x series. Drupal 8.1.x will not receive any further development aside from security fixes. Drupal 8.2.0-rc1 is now available and sites should prepare to upgrade to 8.2.0.

Drupal 8.2.6 was released on February 1, 2017 and is the final full bugfix release for the Drupal 8.2.x series. Drupal 8.2.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.3.0 on April 5, 2017. (Drupal 8.3.0-alpha1 is available for testing.)

Drupal 8.3.6 was released on August 2, 2017 and is the final full bugfix release for the Drupal 8.3.x series. Drupal 8.3.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.4.0 on October 4, 2017. (Drupal 8.4.0-alpha1 is available for testing.)

Drupal 8.4.4 was released on January 3, 2018 and is the final full bugfix release for the Drupal 8.4.x series. Drupal 8.4.x will not receive any further development aside from critical and security fixes. Sites should prepare to update to 8.5.0 on March 7, 2018. (Drupal 8.5.0-alpha1 is available for testing.)